Kingsley is having a rare problem, that of making himself heard. Until he takes a full can of beer and smashes it down on the table, silencing the room.

Scowling, he opens the can - and the frothing upstream sprays him full in the face.

"This," thinks the young Martin, "could go either way."

Much to everyone's relief, Kingsley sees the funny side and begins to laugh.

"For once in his life he had acted humourlessly," writes Martin, "and humour corrected him."

They say the ability to laugh at yourself is a sign of strength, and it's true. I know this because when I'm feeling strong, I can laugh at myself, and when I'm feeling weak, I can't.

Which brings me to Boris Johnson and his misadventure in the river Pool.

Promoting the merits of volunteering, the London mayor dipped his toes into the water, trying to grasp some clumps of invasive weed, only to slip and end up chest-deep.

This was a treat for the cameras, and no bad thing for the London mayor, because if anyone can turn a slap-stick humiliation to their advantage, it's him.

"It was very refreshing," he said later, "and I thoroughly recommend it."

It's telling that while Labour tried to dismiss Johnson as a buffoon in the mayoral election campaign, the public took him to heart. We don't divide neatly into serious people and unserious ones.

Hence Gordon Brown's failure to endear himself to the public by portraying himself as "a serious man for serious times."

A serious man doesn't have to be humourless. And when he tells you that serious is what he is, he merely invites the banana skins to fall across his path.

I'm sure Gordon Brown can be very funny in private. But one of his problems in public has been his failure to take a joke.

Teased in the Commons, he looks like a bullied schoolboy on the brink of tears or violence.

Maybe he just hates being teased by public school boys.

But when Vince Cable compares you to Mr Bean, it behoves you to at least crack a smile.

And remember Tony Blair's speech at the Labour Party conference in 2006?

The proceedings had been overshadowed by hostility between Brown and Cherie Blair.

In his speech, Blair paid tribute to his wife, adding, "At least I don't have to worry about her running off with the bloke next door."
It diffused the tension, as good jokes do.

It didn't make me think any less of Brown, until I learned that he tried to talk Blair out of including it. (At least that's what some Labour insiders said; Brown's camp denied it.)

Does any of this matter, when there's a global financial crisis?

Yes. Especially then. Because an ability to take a joke hints at other qualities - confidence, a sense of proportion, a coolness under pressure, a receptiveness to criticism.

Judge no man, I say, until you've seen how he copes when he slips on a banana skin.

awolstenholme@ywng.co.uk